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SCOTT JAGOW: On this day nine years ago, 150 countries signed the Kyoto Treaty. One of the ideas for reducing greenhouse gases was carbon trading. Here's Jeff Tyler from our Sustainability Desk.

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JEFF TYLER: Only the European Union has managed to get an emissions trading system up and running.

Covering 25 countries and a $10 billion market, the EU trading system has made pollution caps work.

BILLY PIZER: The trading has worked. They've met their targets. They've actually exceeded their targets.

That's Billy Pizer, senior fellow at Resources for the Future, a think tank. But he says companies see a downside.

PIZER: There is definitely some concern that the program is making it more expensive to basically do business in Europe.

And more uncertain. Businesses can't plan long-term since participating countries haven't nailed down emissions targets beyond 2008.

But however flawed, at least the EU has a system. In the rest of the world, carbon emissions trading is still guesswork.

I'm Jeff Tyler for Marketplace.